1. Field of the Invention
The present invention relates to heat exchangers and, more particularly, to recuperators for use with turbines and turbo-alternators.
2. Description of the Prior Art
Many gas turbine engines use a heat exchanger or recuperator to increase the operational efficiency of the engine by extracting heat from the exhaust gas of the engine and preheating the intake air before it is passed to a combustor section of the engine. Typically, a recuperator for a gas turbine engine is annular-shaped in cross section and positioned around the engine. Such “annular” recuperators generally include a core which is commonly constructed of a plurality of relatively thin, flat metal sheets having an angled or corrugated spacer fixedly attached therebetween. The sheets are joined into cells and sealed at opposite sides, forming passages between the sheets. The cells are stacked or rolled and form alternating cold air intake cells and hot air exhaust cells. The hot exhaust air from the engine heats the sheets and the spacers; and the cold air cells are heated by conduction from the sheets and the spacers.
One annular heat exchanger is known from U.S. Pat. No. 5,081,834 to Darragh. The heat exchanger disclosed by the Darragh patent is configured to resist the internal forces and pressures and the thermal stresses inherent from the cyclic operation of a gas turbine engine. The core of the heat exchanger disclosed by the Darragh patent has a plurality of heat recipient passages which have a uniform cross-sectional area throughout the entire length of the passages. In addition, the core has a plurality of heat donor passages which have a uniform cross-sectional area throughout the length of the passages. The heat recipient passages contain a heat recipient fluid during operation and the heat donor passages contain a heat donor fluid during operation. The core includes a plurality of stacked primary cells each defining one of the passages (heat recipient passages or heat donor passages) therein. The cells are secured together forming a generally annular shaped core in cross section. Each of the plurality of cells has an involute curve shape and includes at least a pair of primary surface pleated sheets.
A major disadvantage with heat exchangers such as that disclosed by the Darragh patent is that the heat recipient passages and the heat donor passages are defined by a plurality of metal sheets that extend between an inner diameter of the heat exchanger and an outer diameter of the heat exchanger. Each of these sheets is a potential leak path between the heat donor fluid and the heat recipient fluid, which will degrade the efficiency of the heat exchanger and the power output of the engine.
Accordingly, an object of the present invention is to provide a recuperator for use with a turbine or a turbo-alternator that reduces the possibility of leakage between a heat donor fluid and a heat recipient fluid. It is a further object of the present invention to provide a relatively inexpensive recuperation for use with a turbine or a turbo-alternator.